Reactive liquid based gas storage and delivery systems

ABSTRACT

This invention relates generally to an improvement in low pressure storage and dispensing systems for the selective storing of gases having Lewis acidity or basicity, and the subsequent dispensing of said gases at pressures, e.g., generally below 5 psig and typically below atmospheric pressure, by modest heating, pressure reduction or both. The improvement resides in storing the gases in a reversibly reacted state within a reactive liquid having opposing Lewis basicity or acidity.

BACKGROUND OF THE INVENTION

[0001] Many processes in the semiconductor industry require a reliablesource of process gases for a wide variety of applications. Often thesegases are stored in cylinders or vessels and then delivered to theprocess under controlled conditions from the cylinder. The semiconductormanufacturing industry, for example, uses a number of hazardousspecialty gases such as phosphine (PH₃), arsine (AsH₃), and borontrifluoride (BF₃) for doping, etching, and thin-film deposition. Thesegases pose significant safety and environmental challenges due to theirhigh toxicity and pyrophoricity (spontaneous flammability in air). Inaddition to the toxicity factor, many of these gases are compressed andliquefied for storage in cylinders under high pressure. Storage of toxicgases under high pressure in metal cylinders is often unacceptablebecause of the possibility of developing a leak or catastrophic ruptureof the cylinder.

[0002] In order to mitigate some of these safety issues associated withhigh pressure cylinders, on-site electrochemical generation of suchgases has been used. Because of difficulties in the on-site synthesis ofthe gases, a more recent technique of low pressure storage and deliverysystems has been to adsorb these gases onto a solid support. Thesestorage and delivery systems are not without their problems. They sufferfrom poor capacity and delivery limitations, poor thermal conductivity,and so forth.

[0003] The following patents and articles are illustrative of lowpressure, low flow rate gas storage, and delivery systems.

[0004] U.S. Pat. No. 4,744,221 discloses the adsorption of AsH₃ onto azeolite. When desired, at least a portion of the AsH₃ is released fromthe delivery system by heating the zeolite to a temperature of notgreater than about 175° C. Because a substantial amount of AsH₃ in thecontainer is bound to the zeolite, the effects of an unintended releasedue to rupture or failure are minimized relative to pressurizedcontainers.

[0005] U.S Pat. No. 5,518,528 discloses delivery systems based onphysical sorbents for storing and delivering hydride, halide, andorganometallic Group V gaseous compounds at sub-atmospheric pressures.Gas is desorbed by dispensing it to a process or apparatus operating atlower pressure.

[0006] U.S. Pat. No. 5,704,965 discloses sorbents for use in storagesystems where the sorbents may be treated, reacted, or functionalizedwith chemical moieties to facilitate or enhance adsorption or desorptionof fluids. Examples include the storage of hydride gases such as arsineon a carbon sorbent.

[0007] U.S. Pat. No. 5,993,766 discloses physical sorbents forsub-atmospheric storage and dispensing of fluids in which the sorbentcan be chemically modified to affect its interaction with selectedfluids. For example, a sorbent material may be functionalized with aLewis basic amine group to enhance its sorbtive affinity for B₂H₆(sorbed as BH₃).

[0008] U.S. Pat. No. 6,277,342 discloses a method for deliveringBronsted basic gases via reversibly protonating the gases using at leastone polymer support bearing acid groups. The resulting salt formed fromthe acid/base reaction becomes sorbed to the polymer support.

BRIEF SUMMARY OF THE INVENTION

[0009] This invention relates generally to an improvement in lowpressure storage and dispensing systems for the selective storing ofgases having Lewis basicity or acidity, and the subsequent dispensing ofsaid gases, generally at pressures of 5 psig and below, typically atsubatmospheric pressures, e.g., generally below 760 Torr, by pressuredifferential, heating, or a combination of both. The improvement residesin storing the gases in a reversibly reacted state with a reactiveliquid having Lewis acidity or basicity.

[0010] Several advantages for achieving safe storage, transportation,and delivery of gases having Lewis basicity or acidity can be achieved.These include:

[0011] an ability to maintain a reliable source of these gases whereinthe gases are maintained near or below atmospheric pressure duringshipping and storage;

[0012] an ability to store and deliver gases in essentially pure form;

[0013] an ability to manage the problems associated with the transfer ofheat during gas loading and dispensing;

[0014] an ability to allow for mechanical agitation and pumping, therebymaking operations such as compound transfer more efficient;

[0015] an ability to optimize the binding affinity for a given gasthrough choice of reactive component; and,

[0016] an ability to obtain high gas (or working) capacities compared tothe surface adsorption and chemisorption approaches associated withsolid adsorbents.

BRIEF DESCRIPTION OF THE DRAWING

[0017]FIG. 1 is a schematic perspective representation of a storage anddispensing vessel with associated flow circuitry for the storage anddispensing of gases such as phosphine, arsine, and boron trifluoride.

[0018]FIG. 2 is a graph of working capacity for phosphine for a numberof reactive liquids.

DETAILED DESCRIPTION OF THE INVENTION

[0019] This invention relates to an improvement in a low-pressurestorage and delivery system for gases having Lewis basicity or acidity,particularly hazardous specialty gases such as phosphine, arsine andboron trifluoride, which are utilized in the electronics industry. Theimprovement resides in storing the gases in a continuous liquid mediumby effecting a reversible reaction between a gas having Lewis basicitywith a reactive liquid having Lewis acidity or, alternatively, a gashaving Lewis acidity with a reactive liquid having Lewis basicity.

[0020] The system for storage and dispensing of a gas comprises astorage and dispensing vessel constructed and arranged to hold aliquid-phase medium having a reactive affinity for the gas to be stored,and for selectively flowing such gas into and out of such vessel. Aliquid-phase medium having a reactive affinity for the gas is disposedin the storage and dispensing vessel. A dispensing assembly is coupledin gas flow communication with the storage and dispensing vessel, andconstructed and arranged for selective, on-demand dispensing of the gashaving Lewis acidity or Lewis basicity, by thermal and/or pressuredifferential-mediated evolution from the reactive liquid-phase medium.The dispensing assembly can be constructed and arranged:

[0021] (i) to provide, exteriorly of said storage and dispensing vessel,a pressure below said interior pressure, to effect evolution of the gasfrom the reactive liquid-phase medium, and flow of gas from the vesselthrough the dispensing assembly; and/or

[0022] (ii) to provide means for removal of heat of reaction of the gaswith the reactive liquid and for heating the reactive liquid to effectevolution of the gas therefrom, so that the gas flows from the vesselinto the dispensing assembly.

[0023] Thus, in one aspect, the invention relates to a system for thestorage and delivery of a gas having Lewis basicity, comprising astorage and dispensing vessel containing a reactive liquid having Lewisacidity and having a reactive affinity for the gas having Lewisbasicity. In another aspect, the invention relates to a system for thestorage and delivery of a gas having Lewis acidity, comprising a storageand dispensing vessel containing a reactive liquid having Lewis basicityand having a reactive affinity for the gas having Lewis acidity.

[0024] A further feature of the invention is that the gas reactivelystored within the reactive liquid is readily removable from the reactiveliquid by pressure-mediated and/or thermally-mediated methods. Bypressure-mediated evolution is meant evolution involving theestablishment of pressure conditions, which typically range from 10⁻¹ to10⁻⁷ Torr at 25° C., to cause the gas to evolve from the reactiveliquid. For example, such pressure conditions may involve theestablishment of a pressure differential between the reactive liquid inthe vessel, and the exterior environment of the vessel, which causesflow of the fluid from the vessel to the exterior environment (e.g.,through a manifold, piping, conduit or other flow region or passage).The pressure conditions effecting gas evolution may involve theimposition on the reactive liquid of vacuum or suction conditions whicheffect extraction of the gas from the vessel.

[0025] By thermally-mediated evolution is meant heating of the reactiveliquid to cause the evolution of the gas from the reactive liquid sothat the gas can be withdrawn or discharged from the vessel. Typically,the temperature for thermal-mediated evolution ranges from 30° C. to150° C. Because the complexing medium is a continuous liquid, as opposedto a porous solid medium as employed in the prior art processes, heattransfer is facilitated.

[0026] To facilitate an understanding of the storage and delivery systemin terms of the general description above, reference is made to FIG. 1.The storage and dispensing system 10 comprises storage and dispensingvessel 12 such as a conventional gas cylinder container of elongatecharacter. In the interior volume 14 of such vessel is disposed a liquid16 of a suitable reactivity with the gas to be stored. The vessel 12 isprovided at its upper end with a conventional cylinder head gasdispensing assembly 18, which includes valves, regulators, etc., coupledwith the main body of the cylinder 12 at the port 19. Port 19 allows gasflow from the reactive liquid retained in the cylinder into thedispensing assembly 18. Optionally, the vessel can be equipped with anon/off valve and the regulator provided at the site for delivery.

[0027] The storage and delivery vessel 12 may be provided with internalheating means (not shown) which serves to thermally assist in shiftingthe equilibrium such that the gas bonded to the reactive liquid isreleased. Often, the gas stored in the reactive liquid is at leastpartially, and most preferably fully, dispensed from the storage anddispensing vessel containing the gas by pressure-mediated evolution.Such pressure differential may be established by flow communicationbetween the storage and dispensing vessel, on the one hand, and a vacuumor low pressure ion implantation chamber, on the other. The storage anddelivery vessel 12 may also be provided with a means of agitation (notshown) which serves to enhance the rate of gas diffusion from thereactive liquid.

[0028] The storage and delivery vessel 12 may be used as the reactoritself in that a reactive liquid can be transferred into the vessel andthe gas subsequently added under conditions for forming the reactioncomplex in situ within the vessel. The reactive complex comprised of thereactive liquid and gas can also be formed external to the storage anddelivery system and transferred into the storage vessel 12.

[0029] The key to the process described herein is the use of a reactive,nonvolatile liquid for storage and delivery of the gas having opposingLewis acidity or Lewis basicity to that of the gas. The selection of thereactive liquid for association with the gas, whether Lewis basic orLewis acidic, is to provide for a working capacity within a pressurerange from 20 to 760 Torr of at least 0.5 mole of gas per liter ofliquid, preferably greater than 1 mole of gas per liter of liquid, (e.g.34 grams of PH₃, 78 grams of AsH₃, 28 grams of B₂H₆, or 68 grams of BF₃per liter of liquid), and allow for removal from the reactive liquid ofat least 15%, preferably at least 50%, and most preferably at least 65%of the reacted gas within a working pressure range of from 20 to 760Torr over a temperature range from subambient, e.g., 0° C., to 150° C.

[0030] A suitable reactive liquid has low volatility and preferably hasa vapor pressure below about 10⁻² Torr at 25° C. and, more preferably,below 10⁻⁴ Torr at 25° C. In this way, the gas to be evolved from thereactive liquid can be delivered in substantially pure form and withoutsubstantial contamination from the reactive liquid carrier. Liquids witha vapor pressure higher than 10⁻² Torr may be used if contamination canbe tolerated. If not, a scrubbing apparatus may be required to beinstalled between the liquid sorbent and process equipment. In this way,the reactive liquid can be scavenged to prevent it from contaminatingthe gas being delivered. Ionic liquids have low melting points (i.e.typically below room temperature) and typically decompose beforevaporizing, usually at temperatures above 200° C., which make them wellsuited for this application.

[0031] Ionic liquids can act as a reactive liquid, either as a Lewisacid or Lewis base, for effecting reversible reaction with the gas to bestored. These reactive ionic liquids have a cation component and ananion component. The acidity or basicity of the reactive ionic liquidsthen is governed by the strength of the cation, the anion, or by thecombination of the cation and anion. The most common ionic liquidscomprise salts of alkylphosphonium, alkylammonium, N-alkylpyridinium orN,N′-dialkylimidazolium cations. Common cations contain C₁₋₁₈ alkylgroups, and include the ethyl, butyl and hexyl derivatives ofN-alkyl-N′-methylimidazolium and N-alkylpyridinium. Other cationsinclude pyridazinium, pyrimidinium, pyrazinium, pyrazolium, triazolium,thiazolium, and oxazolium.

[0032] Also known are “task-specific” ionic liquids bearing reactivefunctional groups on the cation. Such ionic liquids can be preparedusing functionalized cations containing a Lewis base or Lewis acidfunctional group, and these ionic liquids can be used here. Taskspecific ionic liquids often are aminoalkyl, such as aminopropyl;ureidopropyl, and thioureido derivatives of the above cations. Specificexamples of task-specific ionic liquids containing functionalizedcations include salts of 1-alkyl-3-(3-aminopropyl)imidazolium,1-alkyl-3-(3-ureidopropyl)imidazolium,1-alkyl-3-(3-thioureidopropyl)imidazolium,1-alkyl-4-(2-diphenylphosphanylethyl)pyridinium,1-alkyl-3-(3-sulfopropyl)imidazolium, andtrialkyl-(3-sulfopropyl)phosphonium.

[0033] A wide variety of anions can be matched with the cation componentof such ionic liquids for achieving Lewis acidity. One type of anion isderived from a metal halide. The halide most often used is chloridealthough the other halides may also be used. Preferred metals forsupplying the anion component, e.g. the metal halide, include copper,aluminum, iron, zinc, tin, antimony, titanium, niobium, tantalum,gallium, and indium. Examples of metal chloride anions are CuCl₂ ⁻,Cu₂Cl₃ ⁻, AlCl₄ ⁻, Al₂Cl₇ ⁻, ZnCl₃ ⁻, ZnCl₄ ²⁻, Zn₂Cl₅ ⁻, FeCl₃ ⁻, FeCl₄⁻, Fe₂Cl₇ ⁻, TiCl₅ ⁻, TiCl₆ ²⁻, SnCl₅ ⁻, SnCl₆ ²⁻, etc.

[0034] As is known in the synthesis of ionic liquids, the type of metalhalide and the amount of the metal halide employed has an effect on theacidity of the ionic liquid. For example, when aluminum trichloride isadded to a chloride precursor, the resulting anion may be in the formAlCl₄ ⁻ or Al₂Cl₇ ⁻. The two anions derived from aluminum trichloridehave different acidity characteristics, and these differing aciditycharacteristics impact on the type of gases that can be reactivelystored.

[0035] Room temperature ionic liquids can be formed by reacting a halidecompound of the cation with an anion supplying reactant.

[0036] Examples of halide compounds from which Lewis acidic or Lewisbasic ionic liquids can be prepared include:

[0037] 1-Ethyl-3-methylimidazolium bromide;

[0038] 1-Ethyl-3-methylimidazolium chloride;

[0039] 1-Butyl-3-methylimidazolium bromide;

[0040] 1-Butyl-3-methylimidazolium chloride;

[0041] 1-Hexyl-3-methylimidazolium bromide;

[0042] 1-Hexyl-3-methylimidazolium chloride;

[0043] 1-Methyl-3-octylimidazolium bromide;

[0044] 1-Methyl-3-octylimidazolium chloride;

[0045] Monomethylamine hydrochloride;

[0046] Trimethylamine hydrochloride;

[0047] Tetraethylammonium chloride;

[0048] Tetramethyl guanidine hydrochloride;

[0049] N-Methylpyridinium chloride;

[0050] N-Butyl-4-methylpyridinium bromide;

[0051] N-Butyl-4-methylpyridinium chloride;

[0052] Tetrabutylphosphonium chloride; and

[0053] Tetrabutylphosphonium bromide.

[0054] When the system is used for storing phosphine or arsine, apreferred reactive liquid is an ionic liquid and the anion component ofthe reactive liquid is a cuprate or aluminate and the cation componentis derived from a dialkylimidazolium salt.

[0055] Gases having Lewis basicity to be stored and delivered from Lewisacidic reactive liquids, e.g., ionic liquids, may comprise one or moreof phosphine, arsine, stibene, ammonia, hydrogen sulfide, hydrogenselenide, hydrogen telluride, isotopically-enriched analogs, basicorganic or organometallic compounds, etc.

[0056] With reference to Lewis basic ionic liquids, which are useful forchemically complexing Lewis acidic gases, the anion or the cationcomponent or both of such ionic liquids can be Lewis basic. In somecases, both the anion and cation are Lewis basic. Examples of Lewisbasic anions include carboxylates, fluorinated carboxylates, sulfonates,fluorinated sulfonates, imides, borates, chloride, etc. Common anionforms include BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, CH₃COO⁻, CF₃COO⁻, CF₃SO₃ ⁻,p-CH₃—C₆H₄SO₃ ⁻, (CF₃SO₂)₂N⁻, (NC)₂N⁻, (CF₃SO₂)₃C⁻, chloride, andF(HF)_(n) ⁻. Other anions include organometallic compounds such asalkylaluminates, alkyl- or arylborates, as well as transition metalspecies. Preferred anions include BF₄ ⁻, p-CH₃—C₆H₄SO₃ ⁻, CF₃SO₃−,(CF₃SO₂)₂N⁻, (NC)₂N⁻(CF₃SO₂)₃C⁻, CH₃COO⁻ and CF₃COO⁻.

[0057] Ionic liquids comprising cations that contain Lewis basic groupsmay also be used in reference to storing gases having Lewis acidity.Examples of Lewis basic cations include N,N′-dialkyimidazolium and otherrings with multiple heteroatoms. A Lewis basic group may also be part ofa substituent on either the anion or cation. Potentially useful Lewisbasic substituent groups include amine, phosphine, ether, carbonyl,nitrile, thioether, alcohol, thiol, etc.

[0058] Gases having Lewis acidity to be stored in and delivered fromLewis basic reactive liquids, e.g., ionic liquids, may comprise one ormore of diborane, boron trifluoride, boron trichloride, SiF₄, germane,hydrogen cyanide, HF, HCl, Hl, HBr, GeF₄, isotopically-enriched analogs,acidic organic or organometallic compounds, etc.

[0059] Nonvolatile covalent liquids containing Lewis acidic or Lewisbasic functional groups are also useful as reactive liquids forchemically complexing gases. Such liquids may be discrete organic ororganometallic compounds, oligomers, low molecular weight polymers,branched amorphous polymers, natural and synthetic oils, etc.

[0060] Examples of liquids bearing Lewis acid functional groups includesubstituted boranes, borates, aluminums, or alumoxanes; protic acidssuch as carboxylic and sulfonic acids, and complexes of metals such astitanium, nickel, copper, etc.

[0061] Examples of liquids bearing Lewis basic functional groups includeethers, amines, phosphines, ketones, aldehydes, nitrites, thioethers,alcohols, thiols, amides, esters, ureas, carbamates, etc. Specificexamples of reactive covalent liquids include tributylborane, tributylborate, triethylaluminum, methanesulfonic acid, trifluoromethanesulfonicacid, titanium tetrachloride, tetraethyleneglycol dimethylether,trialkylphosphine, trialkylphosphine oxide, polytetramethyleneglycol,polyester, polycaprolactone, poly(olefin-alt-carbon monoxide),oligomers, polymers or copolymers of acrylates, methacrylates, oracrylonitrile, etc. Often, though, these liquids suffer from excessivevolatility at elevated temperatures and are not suited forthermal-mediated evolution. However, they may be suited forpressure-mediated evolution.

[0062] To provide an understanding of the concepts disclosed herein thefollowing are relevant definitions to the process:

Definitions

[0063] Total Capacity (or Capacity): Moles of gas that will react withone liter of reactive liquid at a given temperature and pressure.

[0064] Working Capacity (C_(w)): Moles of gas per liter of reactiveliquid which is initially stored and is subsequently removable from theliquid during the dispensing operation, specified for a giventemperature and pressure range, typically at 20 to 50° C. over thepressure range 20 to 760 Torr.

[0065] C_(w)=(moles of reacted gas—moles of gas remaining afterdelivery)/(liters of reactive liquid)

[0066] Percent Reversibility: Percentage of gas initially reacted withthe liquid which is subsequently removable by pressure differential,specified for a given temperature and pressure range, typically at 20 to50° C. over the pressure range 20 to 760 Torr.

[0067] % Reversibility=[(moles of reacted gas—moles of gas remainingafter delivery)/(moles of initially reacted gas)]*100.

[0068] It has been found that good Lewis acid/basic and Lewisbasic/acidic systems can be established from the Gibbs free energy ofreaction (ΔG_(rxn)) for a given system. In a storage and delivery systembased upon a reactive liquid and a gas having Lewis acidity or basicity,a ΔG_(rxn) range exists for operable temperature and pressure and isfrom −1 to about −6 kcal/mole. There also exists an optimum ΔG_(rxn) fora given temperature and pressure range, which corresponds to a maximumworking capacity for the liquid. In reference to the gas PH₃, if themagnitude of ΔG_(rxn), (and thus, K_(eq)) is too small, the reactiveliquid will have insufficient capacity for PH₃. This insufficientcapacity may be compensated for by selecting a reactive liquid with ahigher total capacity (i.e. higher concentration of PH₃ reactivegroups). If the magnitude of ΔG_(rxn) (and thus, K_(eq)) is too large,an insufficient amount of PH₃ will be removable at the desired deliverytemperature. For the reaction of PH₃ with a Lewis acid, A, at 25° C. andin the pressure range 20 to 760 Torr, the optimum value range forΔG_(rxn) is about from −2.5 to −3.5 kcal/mol. For all systems insolution involving the reaction of a single equivalent of gas with asingle equivalent of Lewis acid/base group, the optimum ΔG_(rxn) will beabout −3 kcal/mol at 25° C. and between 20 to 760 Torr. The situation ismore complex for other systems, e.g., if the gas and liquid react togive a solid complex, or if more than one equivalent of a gas reactswith a single equivalent of a Lewis acid/base group.

[0069] One of the difficulties in the development of a suitable storageand delivery system is the matching of a suitable reactive liquid with asuitable gas through prediction of the ΔG_(rxn). To minimizeexperimentation and project the viability of possible systems, quantummechanical methods can be used to elucidate molecular structures.Density Functional Theory (DFT) is a popular ab initio method that canbe used to determine a theoretical value for the change in electronicenergy for a given reaction (ΔE_(rxn)=sum of E_(products)−sum ofE_(reactants)). The following is a discussion for this determination.The calculations are assumed to have an error of approximately ±3kcal/mol.

[0070] The reaction of one equivalent of PH₃ gas with one equivalent ofa Lewis acid acceptor (A) in the liquid phase to give a reaction productin the liquid phase is represented by the equations: $\begin{matrix}\begin{matrix}{{{PH}_{3}({gas})}\overset{K_{1}}{\rightleftharpoons}{{PH}_{3}({soln})}} \\\frac{{A + {{PH}_{3}({soln})}}\overset{K_{2}}{\rightleftharpoons}{A—{PH}}_{3}}{{A + {{PH}_{3}({soln})}}\overset{K_{eq}}{\rightleftharpoons}{A—{PH}}_{3}} \\{K_{eq} = {{K_{1}K_{2}} = \frac{\left\lbrack {A{—PH}}_{3} \right\rbrack}{\lbrack A\rbrack \left\lbrack {{PH}_{3}({gas})} \right\rbrack}}}\end{matrix} & \left( {{Equation}\quad 1} \right)\end{matrix}$

[0071] The equilibrium constant for this reaction, K_(eq), is describedby equation 1. K_(eq) is dependent upon the change in Gibbs free energyfor the reaction, ΔG_(rxn), which is a measure of the binding affinitybetween PH₃ and A. The relationships between ΔG, K, and temperature (inKelvin) are given in equations 2 and 3.

ΔG=ΔH−TΔS  (Equation 2)

ΔG=−RTlnK  (Equation 3)

[0072] The value ΔE_(rxn) can be used as an approximate value for thechange in enthalpy (ΔH, see equation 2). Also, if it is assumed that thereaction entropy (ΔS) is about the same for similar reactions, e.g.,reversible reactions under the same temperature and pressure conditions,the values calculated for ΔE_(rxn) can be used to compare againstΔG_(rxn) for those reactions on a relative basis, i.e., ΔG_(rxn) isapproximately proportional to ΔE_(rxn). Thus, the values calculated forΔE_(rxn) can be used to help predict reactive liquids, including ionicliquids having the appropriate reactivity for a given gas.

[0073] The following examples are intended to illustrate variousembodiments of the invention and are not intended to restrict the scopethereof.

EXAMPLES General Procedure

[0074] The following is a general procedure for establishing theeffectiveness of reactive liquids for storing and delivering gases inthe examples. PH₃ and BF₃ have been used as the descriptive gases forchemical complexation.

[0075] In a glove box, a 25 mL or 50 mL stainless steel reactor wascharged with a known quantity of a liquid. The reactor was sealed,brought out of the glove box, and connected to an apparatus comprising apressurized cylinder of pure PH₃ or BF₃, a stainless steel ballast, anda vacuum pump vented to a vessel containing a PH₃ or BF₃ scavengingmaterial. The gas regulator was closed and the experimental apparatuswas evacuated up to the regulator. Helium pycnometry was used to measureballast, piping and reactor headspace volumes for subsequentcalculations. The apparatus was again evacuated and closed off tovacuum. The following steps were used to introduce PH₃ or BF₃ to thereactor in increments: 1) the reactor was isolated by closing a valveleading to the ballast, 2) PH₃ or BF₃ was added to the ballast (ca. 800Torr) via a mass flow controller, 3) the reactor valve was opened andthe gas pressure was allowed to equilibrate while the reactor contentswere stirred. These steps were repeated until the desired equilibriumvapor pressure was obtained. The quantity of PH₃ or BF₃ added in eachincrement was measured by pressure and volume difference according tothe ideal gas law. The amount of reacted PH₃ or BF₃ was determined bysubtracting tubing and reactor headspace volumes.

EXAMPLE 1 BMlM⁺Al₂Cl₇ ⁻, Lewis Acidic Ionic Liquid for PH₃

[0076] Molecular modeling was used to calculate a binding energy,ΔE_(rxn), for this Lewis acidic ionic liquid with PH₃. The ionic liquidwas modeled as an ion-pair, using 1,3-dimethylimidazolium as the cation,Al₂Cl₇ ₇ ⁻ as the anion, and it was assumed that one equivalent of PH₃reacted per equivalent of Al₂Cl₇ ⁻ anion (concentration of Al₂Cl₇ ⁻=3.2mol/L). Structures were determined based on minimum energy geometryoptimization using Density Functional Theory (DFT) at the BP level witha double numerical (DN**) basis set. This Lewis acidic ionic liquid wascalculated to have a ΔE_(rxn) of 0.71 kcal/mol, which suggests that thereaction is slightly unfavorable, although within the generallimitations of error. To clarify the results of modeling, the followingreaction was run.

[0077] In a glove box, 9.07 g of AlCl₃ (2 equivalents) was slowly addedto 5.94 g (1 equivalent) of 1-butyl-3-methylimidazolium chloride(BMlM+Cl). (It is assumed the anion Al₂Cl₇ ⁻ is formed from the reactionstoichiometry 2 equivalents AlCl₃ to 1 equivalent BMlM⁺Cl⁻) A 25 mLreactor was charged with 4.61 g of BMlM⁺Al₂Cl₇ ⁻ (density=1.2 g/mL) andthe general procedure for measuring PH₃ reaction was followed. The ionicliquid reacted with 6.9 mmol of PH₃ at room temperature and 776 Torr,corresponding to 1.8 mol PH₃/L of ionic liquid.

[0078] The results show % reversibility=89%, working capacity=1.6 mol/L(room temperature, 20-760 Torr). The experimental ΔG_(rxn) isapproximately −1.9 kcal/mol at 25° C.

[0079] These results show that the ionic liquid BMlM⁺Al₂Cl₇ ⁻ iseffective as a reactive liquid for PH₃ and suitable for use in a storageand delivery system as shown in the figure and that the ΔE_(rxn)provides excellent guidance in the selection of a reactive system.

[0080] Delivery of the complex formed to storage and delivery system anbe effected by pumping the complex to the vessel.

EXAMPLE 2 BMlM⁺CuCl₂ ⁻, Lewis Acidic Ionic Liquid For PH₃

[0081] In a glove box, 3.10 g of CuCl was slowly added to a flaskcharged with 5.46 g of BMlM⁺Cl⁻ (1:1 stoichiometry). (It is assumed theanion CuCl₂ ⁻ is formed from the reaction stoichiometry 1 equivalentCuCl to 1 equivalent BMlM⁺Cl⁻). The mixture was stirred overnight andstored. A glass insert was charged with 7.71 g of the ionic liquid(density=1.4 g/mL) and placed into a 50 mL reactor, and the generalprocedure for measuring PH₃ reaction was followed. The Lewis acidicionic liquid reacted with 7.6 mmol of PH₃ at room temperature and 674Torr, corresponding to 1.4 mol PH₃/L of ionic liquid. Equilibrium datapoints were not obtained and % reversibility and working capacity werenot determined. But, this reactive liquid is expected to have a high %reversibility and, thus, a sufficient working capacity for a storage anddelivery system.

EXAMPLE 3 BMlM⁺Cu₂Cl₃ ⁻, Lewis Acidic Ionic Liquid For PH₃

[0082] Molecular modeling was used to approximate the effectiveness ofBMlM⁺Cu₂Cl₃ ⁻ as a reactive liquid. The ionic liquid was modeled as anion-pair, using 1,3-dimethylimidazolium as the cation, Cu₂Cl₃ ⁻ as theanion, and it was assumed that one equivalent of PH₃ reacted with eachequivalent of copper (concentration of Cu reactive groups=9.7 mol/L).Structures were determined based on minimum energy geometry optimizationusing Density Functional Theory (DFT) at the BP level with a doublenumerical (DN**) basis set. This Lewis acidic ionic liquid wascalculated to have an average ΔE_(rxn) of −5.5 kcal/mol for its reactionwith PH₃. The results indicate that this ionic liquid should bind PH₃more strongly than BMlM⁺Al₂Cl₇ ⁻ of Example 1. Since ΔG_(rxn) is smallerin magnitude than ΔE_(rxn) and the optimum ΔG_(rxn) for the pressurerange 20 to 760 Torr at room temperature is ca. −3 kcal/mol, the resultsuggests that the binding properties of BMlM⁺Cu₂Cl₃ ⁻ may be well suitedfor reversibly reacting with PH₃ (i.e., high working capacity and high %reversibility).

[0083] In a glove box, 11.6 g of CuCl was slowly added to a round bottomflask charged with 10.2 g of BMlM⁺Cl⁻ (2:1 stoichiometry). (It isassumed the anion Cu₂Cl₃ ⁻ is formed from the reaction stoichiometry 2equivalents CuCl to 1 equivalent BMlM⁺Cl⁻). The mixture was stirredovernight. A glass insert was charged with 12.02 g of the ionic liquid(density=1.8 g/mL) and placed into a 50 mL reactor, and the generalprocedure for measuring PH₃ reaction was followed. The ionic liquidreacted with 51 mmol of PH₃ at room temperature and 736 Torr,corresponding to 7.6 mol PH₃/L of ionic liquid.

[0084] The results show % reversibility=84%, working capacity=6.4 mol/L(room temperature, 20-736 Torr). The experimental ΔG_(rxn) isapproximately −2.6 kcal/mol at 22° C.

[0085] This reactive liquid outperformed the aluminate-based ionicliquid in Example 1 because it has a higher reactive group concentration(theoretical capacity of 9.7 vs. 3.2 mol/L), and its binding affinityfor PH₃ as calculated by ΔE_(rxn) and measured by ΔG_(rxn) is bettermatched compared toBMlM⁺Al₂Cl₇ ⁻.

EXAMPLE 4 BMlM⁺BF₄ ⁻, Lewis Base Ionic Liquid for PH₃

[0086] A 50 mL reactor was charged with 3.99 g of BMlM⁺BF₄ ⁻ and thegeneral procedure for measuring PH₃ reaction was followed. The ionicliquid is slightly Lewis basic and it does not react with Lewis basicPH₃, demonstrating that a Lewis acidic species as described in Examples1 to 3 is required for reaction with PH₃. The ΔG_(rxn) reaction is ≧0.

EXAMPLE 5 BMlM⁺AlCl₄ ⁻, Acid/Base Neutral Ionic Liquid for PH₃

[0087] A 50 mL reactor was charged with 9.81 g of BMlM⁺AlCl₄ ⁻ formed byadding AlCl₃ to BMlM⁺Cl (1:1 stoichiometry) and the general procedurefor measuring PH₃ reaction was followed. (It is assumed the anion AlCl₄⁻ is formed from the reaction stoichiometry 1 equivalent AlCl₃ to 1equivalent BMlM⁺Cl⁻). The ionic liquid reacted with 0.44 mmol of PH₃,corresponding to about 0.06 mol PH₃/L of ionic liquid. The AlCl₄ ⁻ anionis not Lewis acidic. It is believed that the small amount of PH₃reaction that was observed was likely due to the presence of a smallconcentration of Lewis acidic Al₂Cl₇ ⁻. This example furtherdemonstrates that a Lewis acidic species is required for reaction withPH₃. The {G_(rxn) reaction is ≧0.

EXAMPLE 6 Methanesulfonic Acid, Liquid Bronsted Acid for PH₃

[0088] A 50 mL reactor was charged with 8.81 g of methanesulfonic acid(density=1.35 g/mL) and the general procedure for measuring PH₃ reactionwas followed. The acid reacted with 5.6 mmol of PH₃, corresponding to0.86 mol PH₃/L of liquid.

[0089] The results show % reversibility=75%, working capacity=0.66 mol/L(room temperature, 20-514 Torr). The binding affinity between PH₃ andmethanesulfonic acid is weak, so the total and working capacities aremodest as compared to the reaction systems of Example 1-3 and the %reversibility is high. The system still meets the necessary criteria fora storage and delivery system. The delivered gas, because of the vaporpressure of methanesulfonic acid (˜1 Torr at 25° C.), is contaminatedwith the acid and would require scrubbing prior to use.

EXAMPLE 7 Triflic Acid, Liquid Brønsted Acid for PH₃

[0090] A 50 mL reactor was charged with 4.68 g of triflic acid(density=1.70 g/mL) and the general procedure for measuring PH₃ reactionwas followed. The acid reacted with 14.7 mmol of PH₃, corresponding to5.3 mol PH₃/L of liquid.

[0091] The results show % reversibility=0%, working capacity=0 mol/L(room temperature, 20-721 Torr). The binding affinity between PH₃ andtriflic acid is too strong, so the reaction is irreversible at roomtemperature in the pressure range required. This liquid is too volatilefor thermal-mediated evolution. It may be suited for a Lewis base gashaving less affinity for the reactive liquid. The delivered gas, becauseof the high vapor pressure of triflic acid (8 Torr at 25° C.), would becontaminated with the acid and would require scrubbing prior to use.

EXAMPLE 8 TiCl₄, Volatile Liquid Reactive Compound For PH₃

[0092] A 50 mL reactor was charged with 12.56 g of TiCl₄ (liquid,density=1.73 g/mol), the reactor was cooled to ca. 7° C. in and icebath, and the general procedure for measuring PH₃ reaction was followed.The ionic liquid reacted with 100.3 mmol of PH₃, corresponding to 13.8mol PH₃/L of TiCl₄ at an equilibrium vapor pressure of 428 Torr and atemperature of 12° C.

[0093] The results show % reversibility=41%, working capacity=5.6 mol/L(12° C., 44-428 Torr). The delivered gas, because of the high vaporpressure of the TiCl₄, is contaminated with the volatile titaniumcomplexes and would require scrubbing prior to use.

COMPARATIVE EXAMPLE 9 Comparison of PH₃ Isotherms for Zeolite 5 Å andReactions of Lewis Acids with PH₃

[0094] A series of reaction isotherms for examples 1, 3, 6, 7, and 8were acquired for comparison to a reported isotherm for PH₃ adsorptiononto zeolite 5 Å. The isotherms are shown in FIG. 2.

[0095] In FIG. 2, it is observed that a significant portion of the totalPH₃ adsorbed on zeolite 5 Å cannot be used under normal dispensingconditions because PH₃ is too strongly adsorbed. The adsorption isothermfor zeolite 5 Å indicates a working capacity of 1.9 mol/L with 66%reversibility between 20 and 710 Torr. Approximately ⅓ of the total PH₃remains adsorbed at a pressure below 20 Torr.

[0096] Regarding BMlM⁺Al₂Cl₇ ⁻, it has a lower total capacity andworking capacity (1.6 mol/L between 20 and 760 Torr) than zeolite 5 Å,but 89% of the PH₃ is reversibly bound down to 20 Torr.

[0097] The reaction isotherms obtained for BMlM⁺Cu₂Cl₃ ⁻ show that thisionic liquid has a significantly higher total capacity as well asworking capacity (6.4 mol/L between 20 and 736 Torr) than zeolite 5 Å.The amount of PH₃ that is reversibly bound is also significantly higher(about 84% for BMlM⁺Cu₂Cl₃ ⁻ vs. 66% for zeolite 5 Å in the samepressure range).

[0098]FIG. 2 shows methanesulfonic acid has a low capacity (0.9 mol/L at515 Torr) because it does not react strongly with PH₃; however, almostall of the PH₃ is reversibly reacted.

[0099] Triflic acid has a relatively high capacity (5.3 mol/L at 721Torr), but essentially none of the reacted PH₃ is removable because thereaction (binding affinity) is too strong.

[0100] TiCl₄ reacts with more than a single equivalent of PH₃ and givesa multi-step isotherm. Although TiCl₄ provides a high working capacity(more than 5 mol/L between 44 and 428 Torr), the gas contains impuritiesas a result of the volatility of the titanium species.

EXAMPLE 10 BMlM⁺BF₄ ⁻, Lewis Basic Ionic Liquid for BF₃

[0101] Molecular modeling was used to approximate the effectiveness ofBMlM⁺BF₄ ⁻ as a reactive liquid for the chemical complexation of BF₃.The ionic liquid was modeled as an ion-pair, using1,3-dimethylimidazolium as the cation, and it was assumed that oneequivalent of BF₃ reacted with the anion from each equivalent ofBMlM⁺BF₄ ⁻ (concentration of BF₄ ⁻ reactive groups=5.4 mol/L).Structures were determined based on minimum energy geometry optimizationusing Density Functional Theory (DFT) at the BP level with a doublenumerical (DN**) basis set. This Lewis basic ionic liquid was calculatedto have a ΔE_(rxn) of −5.5 kcal/mol for its reaction with BF₃.

[0102] The modeling results indicate that the binding affinity of thisionic liquid for BF₃ should be similar to the binding affinity betweenBMlM⁺Cu₂Cl₃ ⁻ and PH₃ in Example 3 where ΔE_(rxn) also is calculated tobe −5.5 kcal/mol. Since the reversible reaction between the Lewis acidicBMlM⁺Cu₂Cl₃ ⁻ and Lewis basic PH₃ provides a near optimum workingcapacity, the result suggests that the binding properties of the Lewisbasic BMlM⁺BF₄ ⁻ may be well suited for reversibly reacting with Lewisacidic BF₃ (i.e. high working capacity and high % reversibility).

[0103] In a glove box, a 25 mL stainless steel reactor was charged with8.82 g of BMlM⁺BF₄ ⁻ purchased from Fluka (density=1.2 g/mL), and thegeneral procedure for measuring BF₃ reaction was followed. The ionicliquid reacted with 38.4 mmol of BF₃ at room temperature and 724 Torr,corresponding to 5.2 mol BF₃/L of ionic liquid.

[0104] The results show % reversibility=70%, working capacity=3.6 mol/L(room temperature, 20-724 Torr). The experimental ΔG_(rxn) is −3.4kcal/mol at 22° C. As predicted by molecular modeling, the reactionbetween BMlM⁺BF₄ ⁻ and BF₃ behaved similarly to the reaction betweenBMlM⁺Cu₂Cl₃ ⁻ and PH₃.

EXAMPLE 11 Tetraglyme, Lewis Basic Liquid for BF₃

[0105] Molecular modeling was used to approximate the effectiveness oftetraethyleneglycol dimethylether (tetraglyme) as a reactive liquid.Calculations were carried out using dimethylether and diethylether tomodel the liquid, and it was assumed that one equivalent of BF₃ reactedwith the ether oxygen in both cases. Structures were determined based onminimum energy geometry optimization using Density Functional Theory(DFT) at the BP level with a double numerical (DN**) basis set.Dimethylether was calculated to have a ΔE_(rxn) of −9.1 kcal/mol for itsreaction with BF₃ and diethylether was calculated to have a ΔE_(rxn) of−6.8 kcal/mol for its reaction with BF₃.

[0106] The modeling results indicate that the binding affinity oftetraglyme for BF₃ may be too strong to be useful at ambienttemperature. To confirm the results of modeling, the following reactionwas run.

[0107] In a glove box, a 25 mL stainless steel reactor was charged with8.42 g of tetraethyleneglycol dimethyl ether (tetraglyme) purchased fromAcros (density=1.0 g/mL), and the general procedure for measuring BF₃reaction was followed. The reaction was highly exothermic and reactionwas rapid. The liquid reacted with 103.4 mmol of BF₃ at room temperatureand 765 Torr, corresponding to 12.3 mol BF₃/L of liquid.

[0108] As predicted by molecular modeling, tetraglyme reacts stronglywith BF₃ at room temperature. Essentially none of the chemicallycomplexed BF₃ could be removed under vacuum at room temperature.Elevated temperatures may by useful for evolving the complexed BF₃, butif the delivered gas is contaminated with tetraglyme, the gas mayrequire scrubbing. For applications requiring ambient temperature, thereactive liquid may be better suited for Lewis acids that are weakerthan BF₃.

[0109] In summary, the results show that reactive liquids having Lewisacidity or basicity can be used for storing gases having opposing Lewisbasicity or acidity and delivering such gases in substantially pure format operating pressures from 20 to 760 Torr over a temperature range from0 to 150° C.

[0110] The present invention has been set forth with regard to severalpreferred embodiments, but the full scope of the present inventionshould be ascertained from the claims which follow.

1. In a system for storage and delivery of a gas, said storage anddelivery system comprised of, i) a vessel containing a medium capable ofstoring a gas, and ii) a regulator means for delivery of said gas storedin said medium from said vessel, the improvement selected from the groupconsisting of: storing a gas having Lewis basicity in a reversiblyreacted state within a medium comprised of a reactive liquid havingLewis acidity; and, storing a gas having Lewis acidity in a reversiblyreacted state within a medium comprised of a reactive liquid havingLewis basicity.
 2. The system of claim 1 wherein the reactive liquid forassociation with the gas, having Lewis basicity or Lewis acidity, issufficient to provide for a working capacity within a pressure rangefrom 20 to 760 Torr of at least 0.5 mole of gas per liter of liquid andprovide for evolution from the reactive liquid of at least 15% of thecomplexed gas at the operative temperature ranging from 0 to 150° C. 3.The system of claim 2 wherein at least 50% of the stored gas isremovable within a working pressure range of from 20 to 760 Torr at atemperature from 20 to 50° C.
 4. The system of claim 3 wherein the gasis Lewis basic and the reactive liquid is an ionic liquid having Lewisacidity.
 5. The system of claim 4 wherein the Lewis basic gas isselected from the group consisting of phosphine, arsine, stibene,ammonia, hydrogen sulfide, hydrogen selenide, hydrogen telluride, andisotopically-enriched analogs.
 6. The system of claim 5 wherein theionic liquid having Lewis acidity is comprised of a salt ofalkylphosphonium, alkylammonium, N-alkylpyridinium orN,N′-dialkylimidazolium cation.
 7. The system of claim 6 wherein theanion component of such ionic liquids having Lewis acidity is derivedfrom a metal halide selected from the group consisting of copper,aluminum, iron, zinc, tin, antimony, titanium, niobium, tantalum,gallium, and indium halide.
 8. The system of claim 7 wherein the anioncomponent is a metal chloride salt and the metal for supplying the anioncomponent is selected from the group consisting of CuCl₂ ⁻, Cu₂Cl₃ ⁻,AlCl₄ ⁻, Al₂Cl₇ ⁻, ZnCl₃ ⁻, ZnCl₄ ²⁻, Zn₂Cl₅ ⁻, FeCl₃ ⁻, FeCl₄ ⁻, Fe₂Cl₇⁻, TiCl₅ ⁻, TiCl₆ ²⁻, SnCl₅ ⁻, and SnCl₆ ²⁻.
 9. The system of claim 8wherein the vapor pressure of said reactive liquid, having Lewis acidityis less than 10⁻⁴ Torr at 25° C.
 10. The system of claim 9 wherein thegas having Lewis basicity is selected from the group consisting ofphosphine and arsine.
 11. The system of claim 5 wherein the ionic liquidis a cuprate or aluminate salt of alkylphosphonium, alkylammonium,N-alkylpyridinium and N,N′-dialkylimidazolium cations.
 12. In a systemfor storage and delivery of a gas, said storage and delivery systemcomprised of, i) a vessel containing a medium capable of storing a gas,and ii) a regulator means for delivery of said gas stored in said mediumfrom said vessel, the improvement which comprises: said gas has Lewisbasicity and is in a reversibly reacted state within a medium comprisedof a reactive liquid having Lewis acidity; where said gas is selectedfrom the group consisting of arsine and phosphine and said liquid is anionic liquid having a dialkyl-imidazolium cation and a chlorocuprate orchloroaluminate anion.
 13. The system of claim 12 wherein thedialkylimidazolium cation is 1-butyl-3-methylimidazolium and said anionis selected from the group consisting of Al₂Cl₇ ⁻, CuCl₂ ⁻ and Cu₂Cl₃ ⁻.14. In a system for storage and delivery of a gas, said storage anddelivery system comprised of, i) a vessel containing a medium capable ofstoring a gas, and ii) a means for delivery of said gas stored in saidmedium from said vessel, the improvement which comprises: said gas hasLewis acidity and is selected from the group consisting of diborane,boron trifluoride, boron trichloride, SiF₄, germane, hydrogen cyanide,HF, HCl, Hl, HBr, GeF₄, isotopically-enriched analogs, acidic organic,organometallic compounds and mixtures thereof, and is stored in areversibly reacted state within a medium comprised of a reactive ionicliquid having Lewis basicity employing an anion selected from the groupconsisting of BF₄ ⁻, p-CH₃—C₆H₄SO₃ ⁻, CF₃SO₃ ⁻, (CF₃SO₂)₂N⁻, (NC)₂N⁻(CF₃SO₂)₃C⁻, CH₃COO⁻ and CF₃COO⁻ and a cation selected from the groupconsisting of alkylphosphonium, alkylammonium, N-alkylpyridinium orN,N′-dialkylimidazolium.
 15. The system of claim 14 wherein the vaporpressure of said reactive liquid having Lewis acidity is less than 10⁻⁴Torr at 25° C.
 16. The system of claim 14 wherein the reactive liquidfor association with the gas having Lewis acidity is sufficient toprovide for a working capacity within a pressure range from 20 to 760Torr of at least 0.5 mole of gas per liter of liquid and provide forevolution from the reactive liquid of at least 50% at the operativetemperature ranging from 0 to 150° C.
 17. The system of claim 16 whereinthe Lewis basic gas is boron trifluoride.
 18. The system of claim 17wherein the ionic liquid has a cation component which isdialkylimidazolium and the anion component is BF₄ ⁻.
 19. In a system forstorage and delivery of a gas, said storage and delivery systemcomprised of, i) a vessel containing a medium capable of storing a gasand ii) a means for delivery of said gas stored in said medium from saidvessel, the improvement selected from the group consisting of: storingthe gas having Lewis basicity in a reversibly reacted state within areactive liquid having Lewis acidity wherein the Gibbs Free energy ofreaction between the gas having Lewis basicity within a reactive liquidhaving Lewis acidity is from about −1 to −6 kcal/mol of reactive groupover a temperature range of from 0 to 150° C.; and, storing the gashaving Lewis acidity in a reversibly reacted state within a reactiveliquid having Lewis basicity and wherein the Gibbs Free energy ofreaction between the gas having Lewis acidity within a reactive liquidhaving Lewis basicity is from about −1 to −6 kcal/mol of reactive groupover a temperature range of from 0 to 150° C.
 20. The system of claim 19wherein the Gibbs free energy of reaction is from −2.5 to −3.5 kcal/molebetween said gas and said reactive liquid at 25° C.
 21. The system ofclaim 20 wherein the reactive liquid is an ionic liquid and the anioncomponent of the reactive liquid is a cuprate, aluminate, or borate andthe cation component is derived from a dialkylimidazolium salt.